Study of drying kinetics of quince

The present work aimed at studying the influence of temperature (40, 50 and 60 ºC) and air velocity (0.7, 0.9 and 1.2 m/s) on drying of quince. From the results obtained it was possible to conclude that the quince drying had a similar kinetic behaviour, regardless of the operating conditions. As to the influence of the drying temperature on the process, it was observed that increasing the drying temperature from 40 ºC to 60 ºC leads to a diminishing of 30 % in the drying time. On the other hand the increase in air velocity does not have a proportional effect on the reduction of dimensionless moisture, particularly at higher quince moisture contents. The rate of quince drying is characterised by the absence of the constant drying-rate period followed by falling-rate period, regardless of the conditions. The data for the moisture ratio over time was fitted to different empirical models with the best performances coming from the Modified Page, Henderson & Page and Logarithmic models

Efeito da secagem nos teores de compostos fenólicos e da atividade antioxidante de bananas Musa nana e Musa cavendishii

Bananas e plátanos são hoje cultivadas em todas as regiões tropicais húmidas e constituem o quarto fruto mais cultivado do mundo. A casca da fruta varia de verde profundo a amarelo ou vermelho, enquanto que a polpa varia de branco-marfim para amarelo ou salmão-amarelo. A polpa pode ser firme, adstringente e pegajosa, quando verde, tornando-se escorregadia quando madura. O sabor pode ser leve e doce ou sub-ácido com um tom de maçã. As bananas das cultivares Musa nana (MN) e Musa cavendishii (MC) foram submetidas a secagem para a comparação das suas propriedades com a correspondente fruta em fresco. Os processos de secagem usados foram a secagem em estufa convectiva e a liofilização. Todas as amostras, bananas em fresco e após secagem, foram trituradas e depois foram usadas 5 g de amostra. Subsequentemente, foram realizadas seis extrações sucessivas para cada amostra (três com metanol e três com uma solução de acetona (40% v/v) ), com duração de uma hora cada, feitas com o auxílio de um banho de ultrassons. Para cada extrato foi determinado o conteúdo fenólico por reagente Folin-Ciocalteu, e a capacidade antioxidante foi estimada utilizando os ensaios de ABTS. Os resultados permitiram concluir que os dois tipos de banana estudados apresentaram resultados semelhantes no que diz respeito aos compostos fenólicos totais presentes. Ainda mais, observou-se que a secagem em estufa, para as duas temperaturas testadas (50ºC e 70ºC) diminuiu o teor de fenóis totais (expressos em base seca) relativamente às bananas frescas. A liofilização aumentou o teor de compostos fenólicos das amostras quando comparado a secagem em estufa

Effect of drying on the textural attributes of green pepper and pumpkin.

Pumpkin and bell pepper are very popular in Portuguese cuisine; however, their processed form is scarce in the market. Therefore, the drying, which is one of the oldest methods for preservation of foods, may represent a possible method to commercialize these vegetables. The most popular drying process uses convection though hot air, but the high temperatures can change the composition and nutritional value as well as the organoleptic quality of the products. Despite the high costs and time consuming of freeze drying, this process generates minor changes in colour, flavor, texture, and chemical composition [1]. Apart from the perceived primary characteristics, texture and flavor play also an important role on the acceptability of foods by the consumers. Hence, it is crucial to determine and control the texture of the processed foods. The present work aims to study the effect of freeze-drying and air drying at different temperatures on the texture of pumpkin and green pepper. The texture attributes (hardness, adhesiveness, springiness, cohesiveness, and chewiness) were estimated after measurements made with a texturometer. Measurements to the fresh green pepper were done on both sides of the pepper tissue, that is from the skin (external) and the flesh (internal) sides. Rupture of the skin from the flesh side required a lower force (10.9 N) when compared with the same action from the skin side (13.8 N). The fresh pumpkin was peeled and texture profile analysis was carried out on cylindrical samples removed at 1, 3 and 4 cm of the skin and on axial and radial directions. At each distance of the skin the results show small differences between both directions. The medium values of hardness for fresh pumpkin were 12.4, 20.0 and 32.6 at 4, 3 and 1 cm of the skin, respectively. Generally, the air convection of green pepper at 30 ºC and 70 ºC has a small effect on cohesiveness and springiness but their effect was very pronnonced on hardness (Figure 1). This parameter can be related to the force performed by mastication that takes part during eating. A similar effect was observed in the chewiness. The firmess (hardness) of the green pepper was also very sensitive to freeze drying. As for the pumpkin, both drying processes – convective and freeze drying – have substantialy influenced its firmeness

Variation of physical properties of banana along drying for cvs. Musa nana and Musa cavendishii

Bananas from two different cultivars, Musa nana and Musa cavendishii, were dried by hot air at two different temperatures (50 ºC and 70 ºC) with the purpose of comparing their properties with the corresponding fresh products. Along the drying process, it was possible to conclude that bulk density of both types of banana increased as the water content was diminishing. The results also indicate that drying originated darker products when compared to the fresh ones, with lower L* (luminosity) and b* (yellowness) and with higher a* (intensification of reddish color). These results were obtained for both cultivars under study and the two hot air temperatures (50 ºC and 70 ºC). With respect to texture, it was observed a reduction of hardness, with drying at 70 ºC, higher than 60 % for the two banana varieties, when compared with the fresh fruits. In addition, the values of cohesiveness and springiness are similar among the fresh and dried state, independently of the banana variety and the temperature of drying

Secagem de peras de S. Bartolomeu em estufa solar.

Como alternativa ao processo tradicional de produção de Pêra Passa de Viseu, foi testada a secagem de peras de S. Bartolomeu em estufa solar, com ventilação forçada, em ambiente protegido e condições monitorizadas. Nos ensaios realizados, verificou-se que as condições de secagem das peras no interior da estufa são muito favoráveis, quando comparadas com as condições ambientais do exterior nos mesmos períodos. Foram realizados ensaios em diferentes anos, e em todos os casos os resultados permitiram observar uma redução muito substancial no tempo de secagem, face à duração do processo por secagem tradicional com exposição directa ao sol. É importante realçar que das vantagens conseguidas com a utilização da estufa se destaca a garantia de uma melhor qualidade higio-sanitária, sem comprometer as características do produto final no que respeita aos seus atributos organolépticos

Quantification of browning kinetics and colour change for quince (Cydonia oblonga Mill.) exposed to atmospheric conditions

Because quince is a fruit that shows a very strong tendency for developing an intense browning when exposed to air, even though for short periods of time, the aim of this work was to evaluate the kinetics of colour change for quince exposed to atmospheric air at ambient temperature over a period of 2 hours. The quince was cut into slices that were left exposed to air, and colour measurements were done right after cutting and every five minutes, using a tristimulus colorimeter measuring the CIELab coordinates, L*, a* and b*. The results confirmed that quince suffers a high degree of browning, with total colour difference increasing strongly from 0 to 30 and browning index increasing from 50 to near 140. Furthermore, the major colour changes occurred during the first 30 minutes of exposure. Different models were tested to fit the experimental data and the results showed that the most used models, zero-order and first-order kinetics were totally inadequate in the present case, while the less cited models revealed to be very good at describing the kinetics of colour change for quince: logistic, modified Maskan and exponential rise

Influence of the drying method on the composition of dried pears.

In Portugal, a traditional product named “Pêra Passa de Viseu” is made by direct open air sun exposure. However, this procedure does not comply with modern quality standards, and therefore in the last years some investigation around this product and the production method has been carried out to better understand it and establish alternative production techniques such as a solar stove, a solar drier and a drying tunnel. The chemical properties of the pears obtained by these methods were analyzed and quantified, trying to obtain a product more similar to the traditional one. The results show that the dryings carried out with sun exposure (inside glass) do not produce fruits much different than those dried by the traditional method